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  ALUMINIUM Aluminium is a soft, durable, lightweight, malleable metal with appearance ranging from silvery to dull grey, depending on the surface roughness. Aluminium is nonmagnetic and nonsparking. It is also insoluble in alcohol, though it can be soluble in water in certain forms. The yield strength of pure aluminium is 7–11 !a, while aluminium alloys have yield strengths ranging from ## !a to $## !a. %$&  Aluminium has about one'third the density and stiffness of steel. It is ductile, and easily machined, cast, drawn and e(truded. )orrosion resistance can be e(cellent due to a thin surface layer of aluminium o(ide that forms when the metal is e(posed to air, effectively  preventing further o(idation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper . %$&  This corrosion resistance is also often greatly reduced when many a*ueous salts are present, particularly in the presence of dissimilar metals.Aluminium has nine isotopes, whose mass numbers range from + to +#. nly 7 Al -stable isotope and $ Al -radioactive isotope, t  1/  0 7. 1# 2  y occur naturally3 however, 7 Al has a natural abundance above 44.45. $ Al is  produced from argon in the atmosphere by spallation caused by cosmic'ray   protons.In the 6arths crust, aluminium is the most abundant -8.+5 by weightmetallic element and the third most abundant of all elements -after o(ygen and silicon. %1 &  9ecause of its strong affinity to o(ygen, however, it is almostnever found in the elemental state3 instead it is found in o(ides or silicates. :eldspars, the most common group of minerals in the 6arths crust, are aluminosilicates. ;ative aluminium metal can be found as a minor phase in low o(ygen fugacity environments, such as the interiors of certain volcanoes. %1+&  It also occurs in the minerals  beryl, cryolite, garnet, spinel and tur*uoise. %1 &  Impurities in Al  + , such as chromium or cobalt yield the gemstones ruby and sapphire, respectively. !ure Al  + , known as corundum, is one of the hardest materials known. %1 & Although aluminium is an e(tremely common and widespread element, the common aluminium minerals are not economic sources of the metal. Almost all metallic aluminium is produced from the ore bau(ite -Al  x -< +'  x . 9au(ite occurs as a weathering product of low iron and silica   bedrock in tropical climatic conditions. %1=&  >arge deposits of bau(ite occur in Australia, 9ra?il, @uinea and amaica but the primary mining areas for the ore are in @hana, Indonesia, amaica, Bussia and Curinam. %12&  Cmelting of the ore mainly occurs in Australia, 9ra?il, )anada, ;orway, Bussia and the Dnited Ctates. 9ecause smelting is an energy'intensive process, regions withe(cess natural gas supplies -such as the Dnited Arab 6mirates are becomingaluminium refiners.Although aluminium is the most abundant metallic element in the 6arths crust, it is never found in free, metallic form, and it was once considered a  precious metal more valuable than gold.  ;apoleon III, 6mperor  of :rance, is reputed to have given a ban*uet where the most honoured guests were given aluminium utensils, while the others had to make do with gold. %1$&%17&  The Eashington onument was completed, with the 1## ounce - .8 kg aluminium capstone being put in place on Fecember $, 188=, in an elaborate dedication ceremony. It was the largest single piece of aluminium cast at the time, when aluminium was as e(pensive as silver. %18&  Aluminium has been produced in commercial *uantities for Gust over 1## years.Aluminium is 1##5 recyclable without any loss of its natural *ualities. Becovery of the metal via recycling has become an important facet of the In 6urope aluminium e(periences high rates of recycling, ranging from = 5 of beverage cans, 825 of construction materials and 425 of transport vehicles. % 2& Becycled aluminium is known as secondary aluminium, but maintainsthe same physical properties as primary aluminium. Cecondary aluminium is produced in a wide range of formats and is employed in 8#5 of the alloy inGections. Another important use is for e(trusion.
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